1. Field of the Invention
The present invention relates to a thermal transfer recording medium usable in a thermal transfer recording apparatus such as a printer or a facsimile. In particular, the present invention relates to a thermal transfer recording medium usable for forming a transfer record of high quality without being influenced by the surface conditions of the paper to which the image is to be transferred.
2. Description of the Related Arts
A thermal transfer recording system comprises placing a thermal transfer recording medium comprising a support, in sheet form, coated with at least one heat-fusible ink layer onto a paper to which the image is to be transferred in such a manner that the heat-fusible ink layer is brought into contact with the paper. The ink layer is then melted by heating the support side of the recording medium with a heating head to transfer the image to the paper. This method has become widely used, since the operability maintenance of the apparatus are excellent, its noise is low and the image can be transferred to plain paper.
However, the above-described heat-fusible ink used heretofore has a problem in that the binder thereof mainly comprises a was. Since the softening of the wax causes the fused ink to be transferred to the surface of a paper, the transferred image is influenced by the surface conditions of the paper. In particular, the viscosity of the wax is seriously reduced by heat and its fused viscosity is very low, so that when the surface of the paper to which the image is to be transferred is uneven, the area of contact of the ink with the recessed part is only small. For example, when the Bekk smoothness of the paper surface is 30 to 40 sec or less, the ink cannot be uniformly spread over the paper which impairs the quality of the image.
When the thickness of the ink is increased to increase the quantity of the ink placed on a particular point of the paper, the ink covers the surface of the paper without fail to solve the problem of an insufficient density of the image or blur due to incomplete transfer of the ink. However, on the other hand, blotting is accelerated to increase the dot size, thereby impairing the resolution and reducing the quality of the image.
Although, the use of a resin as a binder for the heat-fusible inks is known from Japanese Patent Laid-Open Nos. 87234/1979, 163014/1979, 98269/1981 and 130887/1987, its performance is yet unsatisfactory.